Recently, a storage system including a de-duplicate function attracts attention for storage capacity saving or the like and is getting popular. For example, a NAS (Network Attached Storage) or a storage apparatus has the de-duplicate function. Regarding files (data files) to be stored or already stored in a storage area of the storage apparatus, the de-duplicate function detects and de-duplicate files having the same content (data body except for metadata or the like), for example, duplicate files or the like. That is, as control of de-duplicate, the de-duplicate function works, for a plurality of files having the same content to be stored, to restrict the number of storing to storage areas to be once or to unify the files to one common file (a representative file) and store it. Thereby, input/output to a storage area and storage capacity are saved. As a concept or term similar to de-duplicate, there are “Single Instance Store,” unifying, and the like.
Further, in the storage system providing the full-text search function, the full-text search function (full-text search server or the like) performs a processing for reading files in a search target file group from a storage apparatus to create index information for full-text search. The full-text search function searches for the index information in response to a search instruction/request from a host apparatus to return the search result thereto.    U.S. Pat. No. 5,813,008 (Patent Document 1) describes a technique for de-duplicate. In the technique, the index information for search is exempt from de-duplicate (unifying).    U.S. Pat. No. 6,389,433 (Patent Document 2) describes a file server including a de-duplicate function.